1. Field of the Invention
The present invention relates to a friction material used in a brake, or the like, and particularly to a friction material in which the strength of protrusions acting to hold the friction material on a pressure plate can be made large.
The present application is based on Japanese Patent Application No. Hei. 10-65512, which is incorporated herein by reference.
2. Description of the Related Art
A friction material mainly used in a brake, or the like, generally contains, as compounding ingredients, a filler selected from various kinds of fillers, a fibrous reinforcement selected from various kinds of fibers, an abrasive, and a friction modifier such as graphite, metal powder, or the like, and further contains a resin selected from various kinds of resins as a binder for binding these components.
As the amount of resin in the mixture increases, both density and strength of the friction material after molding increase. However, the amount of resin is generally suppressed to be as small as in a range of from about 5% by weight to about 15% by weight because both moderate plasticity and the presence of pores are required in terms of friction performance.
On the other hand, when the friction material is used for a brake, a structure in which the friction material is held by means of adhesively bonding the friction material to a back plate, or the like, is formed as a brake pad. The structure is as shown in FIG. 4. Because the brake pad 1 has such a structure, an idea for holding the friction material 2 firmly is applied to the back plate 3. That is, a plurality of holes 5 are provided in the back plate. The friction material 2 is preformed so that protrusions 4 are formed in positions corresponding to those of the holes 5. The preformed friction material is put on the back plate and heat-molded. The friction material 2 is integrally bonded to the back plate in the condition that the protrusions 4 are fitted into the holes 5 of the back plate, so that the brake pad 1 is produced.
In this occasion, the rear surface of the friction material 2 is adhesively bonded to the back plate firmly to thereby attach the friction material 2 to the back plate.
As described above, to suppress generally the amount of resin in the friction material to be as small as in a range of from about 5% by weight to about 15% by weight is preferable in terms of friction performance. However, there is a tendency to reduce the density and strength of the protrusions 4 because components hardly-flow in the protrusions 4. Further, there is a tendency to reduce the density of friction material portions above the protrusions because of the influence of the reduction of the density and strength of the protrusions. That is, rough portions 6 are formed. There is a problem that it is difficult to provide a friction material having uniform density as a whole.